Voltage-to-current architecture and error correction schemes

ABSTRACT

Certain aspects of the present disclosure are generally directed to circuitry and techniques for voltage-to-current conversion. For example, certain aspects provide a circuit for signal amplification including a first amplifier; a first transistor, a gate of the first transistor being coupled to an output of the first amplifier and a drain of the first transistor being coupled to an output node of circuit; a first resistive element coupled between a first input node of the circuit and an input of the first amplifier; a second amplifier; a second transistor, a gate of the second transistor being coupled to an output of the second amplifier and a drain of the second transistor being coupled to the output node of circuit; and a second resistive element coupled between a second input node of the circuit and an input of the second amplifier.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of and priority to U.S. ProvisionalApplication No. 62/965,542, filed Jan. 24, 2020, which is herebyexpressly incorporated by reference herein in its entirety as if fullyset forth below and for all applicable purposes.

FIELD

The present disclosure relates to audio signal processing, and morespecifically, to circuitry for voltage-to-current conversion.

BACKGROUND

A speaker is a transducer that produces a pressure wave in response toan input electrical signal, and thus, sound is generated. The speakerinput signal may be produced by an audio amplifier that receives arelatively lower voltage analog audio signal and generates an amplifiedsignal (with a relatively higher voltage) to drive the speaker. Adynamic loudspeaker is typically composed of a lightweight diaphragm (acone) connected to a rigid basket (a frame) via a flexible suspension(often referred to as a spider) that constrains a voice coil to moveaxially through a cylindrical magnetic gap. When the input electricalsignal is applied to the voice coil, a magnetic field is created by theelectric current in the coil, thereby forming a linear electric motor.By varying the electrical signal from the audio amplifier, themechanical force generated by the interaction between the magnet and thevoice coil is modulated and causes the cone to move back and forth,thereby creating the pressure waves interpreted as sound.

SUMMARY

Certain aspects of the present disclosure are generally directed tocircuitry and techniques for current sensing, such as sensing current toa speaker in an audio application.

Certain aspects of the present disclosure are directed to a circuit forsignal processing. The circuit generally includes a first amplifier; afirst transistor, a gate of the first transistor being coupled to anoutput of the first amplifier and a drain of the first transistor beingcoupled to an output node of circuit; a first resistive element coupledbetween a first input node of the circuit and an input of the firstamplifier, the first resistive being further coupled between the inputnode and a source of the first transistor; a second amplifier; a secondtransistor, a gate of the second transistor being coupled to an outputof the second amplifier and a drain of the second transistor beingcoupled to the output node of circuit; and a second resistive elementcoupled between a second input node of the circuit and an input of thesecond amplifier, the second resistive element being further coupledbetween the other input node and a source of the second transistor.

Certain aspects of the present disclosure are directed to a method forsignal processing. The method generally includes generating a firstcurrent through a first resistive element by driving, via a firstamplifier, a gate of a first transistor based on a first voltage at afirst input node, wherein the first resistive element is coupled betweenthe first input node and an input of the first amplifier; providing thefirst current to an output node, a drain of the first transistor beingcoupled to the output node; generating a second current through a secondresistive element by driving, via a second amplifier, a gate of a secondtransistor based on a second voltage at a second input node, wherein thesecond resistive element is coupled between the second input node and aninput of the second amplifier; and providing the second current to theoutput node, a drain of the second transistor being coupled to theoutput node.

Certain aspects of the present disclosure are directed to an apparatusfor signal processing. The apparatus generally includes means forgenerating a first current through a first resistive element by drivinga gate of a first transistor based on a first voltage at a first inputnode; means for providing the first current to an output node; means forgenerating a second current through a second resistive element bydriving a gate of a second transistor based on a second voltage at asecond input node; and means for providing the second current to theoutput node.

In some aspects, the apparatus may also include: means for generating athird current through a third resistive element by driving a gate of athird transistor based on a third voltage at a third input node; meansfor providing the third current to another output node; means forgenerating a fourth current through a fourth resistive element bydriving a gate of a fourth transistor based on a fourth voltage at afourth input node; and means for providing the fourth current to theother output node. In some aspects, a voltage difference between thefirst input node and the third input node represents a first currentflow, and a voltage difference between the second input node and thefourth input node represents a second current flow. In some aspects, thefirst current flow comprises a current through a first signal path of anH-bridge amplifier, and the second current flow comprises a currentthrough a second signal path of the H-bridge amplifier.

In some aspects, the apparatus may also include: means for sensing anaverage between the first and third voltages at the first input node andthe third input node; and means for setting a common-mode voltageassociated with the means for generating the first current based on theaverage between the first and third voltages. In certain aspects, theapparatus may also include: means for sensing an average between thefirst and third voltages at the first input node and the third inputnode; and means for setting a voltage at a body terminal of a transistorused to implemented the first resistive element based on the averagebetween the first and third voltages.

In certain aspects, the apparatus may also include means for calibratingfor a mismatch between the first resistive element and the secondresistive element by adjusting a resistance between the second inputnode and an input of the means for generating the first current. In someaspects, the apparatus may also include means for compensating for anerror current flow to the output node by selectively coupling one ormore capacitive elements between the output node and one of a voltagerail node and an electric ground node. The voltage rail node may have avoltage that is a fraction of a supply voltage for the means forgenerating the first current.

Certain aspects of the present disclosure are directed to an amplifiercircuit. The amplifier circuit generally includes: an amplifiercomprising a first switch, a second switch, a first resistor coupled tothe first switch, and a second resistor coupled to the second switch; afirst sensing path configured to convert a first voltage across thefirst resistor to a first sensed current; a second sensing pathconfigured to convert a second voltage across the second resistor to asecond sensed current; and a summing amplifier configured to sum thefirst and second sensed currents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example audio amplifier system, in accordance withcertain aspects of the present disclosure.

FIG. 2 illustrates a circuit for voltage-to-current conversion, inaccordance with certain aspects of the present disclosure.

FIG. 3 illustrates a circuit for voltage-to-current conversionimplemented with resistor calibration networks and capacitivecalibration networks, in accordance with certain aspects of the presentdisclosure.

FIG. 4 is a flow diagram illustrating example operations for signalprocessing, in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Certain aspects of the present disclosure are generally directed tocircuitry and techniques for current sensing. For example, drive currentfor a speaker may be sensed for temperature control. Certain aspectsprovide voltage-to-current circuitry and error correction circuitry forthe current sensing, as described in more detail herein.

FIG. 1 illustrates an example audio amplifier system 100 (also referredto as an “audio system”), in accordance with certain aspects of thepresent disclosure. As illustrated, a digital signal processor (DSP) 102may receive and process audio signals 114 (e.g., a digital audio signal)by applying a digital filter aimed at increasing audio quality. Thefiltered digital signal 120 produced by the DSP (or a further processedversion thereof) may be used to control an amplifier 110 to generate anamplified signal 122. The amplified signal 122 may drive a speaker 112to produce an acoustic output (e.g., sound waves) 124.

High output volume in mobile devices is becoming more and more importantin next-generation mobile devices. Higher volume directly translates tohigher output power. The higher volumes may be difficult to achieve withthe relatively low voltages provided by lithium-ion batteries.Therefore, on-chip boost switchers may be used to boost the batteryvoltage to a higher level that supplies the speaker power amplifier(e.g., amplifier 110). The amplifier 110 may be implemented as a class-Damplifier due to the relatively high power efficiency associated withclass-D amplifiers compared to other amplifier classes. The efficiencyof the class-D amplifier may be further improved by implementing theclass-D amplifier in an H-bridge configuration, as described below withrespect to FIG. 2.

In certain aspects, a speaker protection module 140 may be used to sensea drive current for the speaker 112, and provide a digitalrepresentation of the current to the DSP 102 for speaker protection.Speaker protection modules (e.g., module 140) may have multiplefunctions. For example, speaker protection modules may sense the speakercoil temperature and, in combination with the DSP 102, control the gainof an amplifier (e.g., amplifier 110) to avoid coil burnout. Thetemperature of the speaker coil may be proportional to direct-current(DC) resistance of the coil, and thus the sensed drive current for thespeaker 112 may be used as a temperature sense mechanism in order tocontrol the gain of the amplifier. Additionally or alternatively,speaker protection modules may provide impedance measurement to sensethe resonant frequency of the speaker coil and provide excursion controlto avoid damage to the speaker membrane. Accurate voltage/current (V/I)sensing in the presence of strong class-H modulation (e.g., used toachieve high efficiency in speaker drivers) can be difficult to achieve.

Certain aspects of the present disclosure provide a voltage-to-current(V2I) architecture for current sensing, as described in more detailherein. The V2I architecture described herein may provide improveddistortion performance in the presence of strong class-H modulation, ascompared to conventional implementations.

FIG. 2 illustrates an example V2I circuit 200, in accordance withcertain aspects of the present disclosure. As illustrated, an H-bridgeamplifier 202 (e.g., corresponding to the amplifier 110) may be used todrive a speaker (e.g., speaker 112), represented by the resistiveelement 281 (e.g., an 8Ω speaker). As illustrated, the amplifier 202includes switches 204, 206, 208, 210 and current-sensing resistiveelements 212, 214 (also referred as “current sense resistive elements”)coupled in series with respective switches 206, 210. The switches 204,206, 208, 210 may be controlled based on the digital signal 120 (or afurther processed version thereof). In some aspects, the switches 204,206 may be implemented using p-type metal-oxide-semiconductor (PMOS)transistors and the switches 208, 210 may be implemented using n-typemetal-oxide-semiconductor (NMOS) transistors. The current-sensingresistive element 212 may be coupled between V2I circuit input nodes272, 274, and the current-sensing resistive element 214 may be coupledbetween V2I circuit input nodes 211, 213. The V2I circuit input node 272may be coupled to the voltage rail VDD and the V2I circuit input node213 may be coupled to a reference potential node VSS. The voltage acrossthe current-sensing resistive elements 212, 214 may be sensed andconverted to a current by the V2I circuit 200, the sensed voltagesrepresenting the drive current of the speaker.

The V2I circuit 200 may include an amplifier 220 having a positiveoutput driving a gate of a transistor 222 and a negative output drivinga gate of a transistor 224. Moreover, a sense path of the V2I circuit200 may include resistive elements 226, 228, 230 (collectively referredto as “R1”), and another sense path of the V2I circuit 200 may includeresistive elements 232, 234, 236 (collectively referred to as “R2”).While R1 and R2 are each illustrated in FIGS. 2 (and 3) as beingimplemented using three restive elements, any number of resistiveelements may be used. The sense paths having the resistive elements R1and R2 may be referred to as the positive sense path of the V2I circuit200. The amplifier 220 may be coupled to a voltage rail VDD (e.g., apositive supply voltage) and a voltage rail VDDL (e.g., a negativesupply voltage), wherein VDDL is less than VDD, for example by 1.8V. Inother words, although not shown in FIG. 2, the positive supply voltageof amplifier 220 may be VDD and the negative supply voltage of theamplifier 220 may be VDDL.

The amplifier 220 senses the voltage at nodes 240, 242, and drives thegates of transistors 222, 224 to sink a current 245 across R1, and acurrent 247 across R2, in effect converting the voltage across theresistive element 212 to currents 245, 247.

Currents 245, 247 are provided to respective output nodes 256, 258 ofthe V2I circuit 200. For example, drains of transistors 222, 224, 250,252 may be electrically coupled to corresponding output nodes 256, 258.The transistors 250, 252 may be implemented as n-typemetal-oxide-semiconductor (NMOS) transistors. Moreover, each oftransistors 222, 224 may be implemented as a p-typemetal-oxide-semiconductor (PMOS) transistor. The output nodes 256, 258are coupled to respective input nodes of a summing amplifier 254 togenerate positive and negative current sense outputs (Isense_Outp,Isense_Outn) at output nodes 295, 297. Similarly, the amplifier 244senses the voltage at nodes 246, 248 and drives transistors 250, 252 toconvert the voltage across the resistive element 214 to a currentflowing across the resistive elements 257, 259, 260 (collectivelyreferred to as “R3”) and a current across resistive elements 262, 264,266 (collectively referred to as “R4”). The sense paths having theresistive elements R3 and R4 may be referred to as the negative sensepath of the V2I circuit 200. The currents associated with the positiveand negative sense paths are effectively summed at output nodes 256, 258and provided to the amplifier 254 for generating Isense_Outp andIsense_Outn. The output of the summing amplifier 254 may be used todrive an analog-to-digital converter (ADC) for providing a digitalsignal to a DSP (e.g., DSP 102) to be used for speaker protection.

As used herein, an input common-mode voltage (VICM) (e.g., at an inputcommon-mode node) of an amplifier generally refers to an average ofvoltages applied to inputs of the amplifier. In certain aspects,resistive elements 268, 270 may be coupled between input nodes 272, 274,a high-side (HS) VICM node (labeled “VICM_HS”) between the resistiveelements 268, 270 being coupled to a body terminal (e.g., bulk terminal)of transistors used to implement R1 and R2, for example to reducenon-linearity associated with R1 and R2. In other words, the bulk of thetransistors used to implement R1 and R2 may be driven based on theaverage of the voltages at input nodes 272, 274 to reduce thenon-linearity associated with R1 and R2 due to conductivity modulation.Similarly, a node (labeled “VICM_LS”) between resistive elements 277,279 (which may be coupled between input nodes 211, 213) may be used todrive the body of transistors used to implement R3 and R4. The voltageat VICM_HS corresponds to the VICM of amplifier 220 (or amplifier 294),and the voltage at VICM_LS corresponds to the VICM of amplifier 244.

In certain aspects, a high-voltage (HV) cascode device may be used forvoltage protection for transistors 224, 222. For example, the HV cascodedevice may include an amplifier 294 that may be used to drive gates oftransistors 296, 298 coupled between respective transistors 224, 222 andrespective output nodes 256, 258. Each of transistors 296, 298 may beimplemented as a PMOS transistor. The transistors 296, 298 are coupledin cascode with transistors 224, 222, respectively. The amplifier 294may be implemented for voltage isolation. For example, the transistors222, 224 may be implemented as low-voltage devices that provide betterlow-noise performance (e.g., as compared to high-voltage devices)allowing for a more accurate voltage-to-current conversion. Thetransistors 296, 298 may be implemented as high-voltage devices andcoupled between respective output nodes 256, 258 and respectivetransistors 224, 222, reducing the voltage applied across thelow-voltage transistors 224, 222.

In certain aspects, input common-mode tracking may be implemented tomitigate common-mode-to-differential-mode (CM2DM) conversion due toresistance mismatch (e.g., resistance mismatch between R1 and R2). Forexample, resistive elements 276, 278 and resistive elements 280, 282 maybe coupled between input nodes 272, 274, as illustrated. A currentsource 288 may be used to sink a current from a VICM cascode node(labeled “VICM_Casc”) between resistive elements 276, 278 to a referencepotential node VSSP, and a current source 290 may be used to sink acurrent from a high-side (HS) reference voltage node (labeled “HS_REF”)between resistive elements 280, 282, in effect setting an inputcommon-mode voltage (e.g., at an input common-mode node) of theamplifiers 220, 294. In other words, the voltage at the VICM_Casc nodebetween resistive elements 276, 278 may be provided to input 293 of theamplifier 294 to be used as a reference voltage for the amplifier 294,and the voltage at the HS_REF node between the resistive elements 280,282 may be provided to input 291 of the amplifier 220 to be used as areference voltage for the amplifier 220. Similarly, a current source 292may be used to source a current from an analog voltage rail (AVDD) to alow-side (LS) reference voltage node (labeled “LS_REF”) betweenresistive elements 284, 286 to set an input common-mode voltage of theamplifier 244. In other words, the voltage at the LS_REF node betweenresistive elements 284, 286 may be provided to input 299 of amplifier244 to be used as a reference voltage for the amplifier 244. In certainaspects, one or more capacitive elements 231, 233, 235, 237 may beimplemented for filtering. In some aspects, AVDD may be a differentvoltage rail than VDD. In some aspects, VSSP may be a differentreference potential node than VSS. In some aspects, the voltage providedat VDD may be the same as the voltage provided at VDD and/or the voltageprovided at VSS may be the same as the voltage provided at VSSP even ifthese voltages are supplied at different voltage rails and/or nodes.

FIG. 3 illustrates the V2I circuit 200 implemented with resistorcalibration networks 302, 304 and capacitive calibration networks 306,308, in accordance with certain aspects of the present disclosure. Whilethe V2I circuit 200 is implemented with both a resistor calibrationnetwork and a capacitive calibration network to facilitateunderstanding, the aspects of the present disclosure may be implementedwith only a resistor calibration network, only a capacitive calibrationnetwork, or both. The resistor calibration networks 302, 304 may beconfigured to compensate, or at least adjust, for resistance mismatchbetween the positive and negative sense paths. For example, a gainmismatch may be present between the positive and negative sense paths ifthe series resistance associated with R2 is not matched with the seriesresistance associated with R3, and/or if the series resistanceassociated with R1 is not matched with the series resistance associatedwith R4. The gain error may manifest as second harmonic distortion atthe output of the V2I circuit 200.

The resistor calibration network 302 includes resistive elements 336,338, 340 coupled in series between the resistive element 230 and thetransistor 222, and resistive elements 330, 332, 334 coupled in seriesbetween the resistive element 236 and the transistor 224. While theresistor calibration network 302 is implemented using three resistiveelements on each sense path (e.g., resistive elements 336, 338, 340),any number of resistive elements may be used. Similarly, while theresistor calibration network 304 is implemented using three resistiveelements on each sense path (e.g., resistive elements 310, 312, 314),any number of resistive elements may be used. As illustrated, thenegative and positive inputs of the amplifier 220 may be coupled to anode between the resistive elements 336, 338 and a node between theresistive elements 330, 332, respectively.

The resistor calibration network 304 includes resistive elements 310,312, 314 coupled in series between the resistive element 260 and thetransistor 250, and resistive elements 316, 318, 320 coupled in seriesbetween the resistive element 266 and the transistor 252. The resistorcalibration network 304 may also include switches 322, 328, 324, 326.The positive input of the amplifier 244 may be selectively coupled to anode between resistive elements 310, 312 or a node between resistiveelements 312, 314 by closing one of switches 322, 328, and the negativeinput of the amplifier 244 may be selectively coupled to a node betweenresistive elements 316, 318 or a node between resistive elements 318,320 by closing one of switches 324, 326. Thus, during calibration, oneof switches 322, 328, and one of switches 324, 326 may be closed tocompensate for (or at least reduce) the gain error that would otherwisebe caused by the resistance mismatch in the positive and negative sensepaths. The series resistive elements of the resistor calibrationnetworks allow for the option to calibrate the gain error between thepositive and negative paths to achieve reduced distortion (e.g., lessthan −95 dB distortion), in some cases. Moreover, the switches 322, 324,326, 328 carry little to no current, and thus, may be implemented usingsimple switch design.

In certain aspects, capacitive elements may be coupled to a highimpedance node (e.g., nodes 256, 258) of the V2I circuit 200 forcapacitive calibration. There may be strong second harmonics on highimpedance nodes (e.g., nodes 256, 258) of the amplifier structure (e.g.,H-bridge amplifier 202) due to the class-H tracking scheme. In otherwords, a second harmonic signal may be present at the supply voltage VDDof the H-bridge amplifier 202. Capacitive mismatch (an example of whichis described below) may cause error current to flow to the output of theamplifier structure (e.g., at nodes 256, 258) and result in secondharmonics at the output of the V2I circuit 200. In certain aspects ofthe present disclosure, current may be injected with polarity oppositeto the error current (e.g., to nodes 256, 258 via capacitive calibrationnetworks 306, 308) to cancel out (or at least reduce) the error currentintroduced due to systematic layout mismatch.

For example, capacitive calibration networks 306, 308 may includecapacitive elements 350, 352, 354, 356, 358, 360, each of which may beselectively coupled to a voltage rail (labeled “VDD/20,” although othervoltages may be used; in some aspects, two or more capacitors in thenetwork 306 and/or 308 are coupled to different voltages or voltagerails) or a ground node (e.g., a reference potential node). There may beparasitic capacitance, which is represented by capacitor 341 in FIG. 3,between the voltage rail VDD and the source of the transistor 222,causing an error current having a strong second harmonic to flow to thenode 258. The capacitive calibration network 308 may be configured tocompensate, or at least adjust, for impact of the current flow due tothe parasitic capacitance 341. For example, one or more of thecapacitive elements 350, 352, 354 may be coupled between node 258 andthe voltage rail (or plurality of voltage rails) by closing one or moreof switches 362, 364, 366, and opening one or more correspondingswitches 363, 365, 367. Similarly in the capacitive calibration network306, one or more of switches 372, 374, 376 may be closed, and acorresponding one or more of switches 373, 375, 377 may be opened, tocompensate, or at least adjust, for parasitic capacitance impacting thecurrent flow to node 256. The switches described and shown in FIG. 3 maybe controlled by a controller, such as the digital signal processor 102described with respect to FIG. 1.

In certain aspects, capacitor values of the capacitive calibrationnetworks 306, 308 may be scaled up, and the calibration voltage railvalue (e.g., VDD/20) for the capacitive calibration networks may bescaled down, allowing for good matching of the capacitive elements withthe parasitic capacitance (e.g., parasitic capacitance 341) of the V2Icircuit and de-sensitizing the effect of having a class-H voltageapplied to the high impedance node of the V2I circuit. For example, thevoltage rail VDD/20 may be a fraction (e.g., 1/20, or any other fractionsuch as 1/10) of the voltage rail VDD of the V2I circuit 200, allowingthe capacitive elements 350, 352, 354, 356, 358, 360 to be implementedwith a higher capacitance as compared to the parasitic capacitance 341.In other words, it may be difficult to implement each of the capacitiveelements 350, 352, 354, 356, 358, 360 to have a capacitance that is assmall as the parasitic capacitance 341. Therefore, the voltage rail nodeVDD/20 to which the capacitive elements are selectively coupled may beset as a fraction of the voltage rail VDD, allowing each of thecapacitive elements 350, 352, 354, 356, 358, 360 to be implemented witha higher capacitance as compared to the parasitic capacitance 341. Thecapacitive calibration networks 306, 308 may be controlled to track theerror current for different operating frequencies (in some cases, forall operating frequencies) of the V2I circuit 200.

While each of the example capacitive calibration networks 306, 308 areillustrated as being implemented with three capacitive elements tofacilitate understanding, any number of capacitive elements may be used.For example, the example capacitive calibration networks 306, 308 may beimplemented using less than or greater than three capacitive elements.Further, any other means of selectively coupling a capacitive element toa high impedance node of the circuit 200 and/or of varying a capacitancecoupled to a high impedance node may be implemented. For example, avariable capacitive element may be coupled between a voltage rail (e.g.,VDD or a fraction thereof) and the node 256 or 258.

The V2I circuit described herein may provide less than −80 dB distortionperformance within an audio band with class-H modulation. Moreover,since the summing associated with the V2I circuit happens in the currentdomain, fewer passive components may be used, resulting in less errorand distortion sources as compared to conventional implementations. TheV2I circuit may also provide a low cost trimming mechanism (e.g.,calibration) to further improve performance. While some examplesprovided herein have been described with respect to an audio amplifierto facilitate understanding, the aspects described herein may beimplemented for any suitable application where a V2I circuit may beused.

FIG. 4 is a flow diagram illustrating example operations 400 for signalprocessing, in accordance with certain aspects of the presentdisclosure. The operations 400 may be performed by a signal processingsystem, such as the V2I circuit 200 and/or H-bridge amplifier 202.

The operations 400 begin, at block 402, with the signaling processingsystem generating a first current (e.g., current 245) through a firstresistive element (e.g., R1) by driving, via a first amplifier (e.g.,amplifier 220), a gate of a first transistor (e.g., transistor 222)based on a voltage at a first input node (e.g., input node 272). In someaspects, the first resistive element may be coupled between the firstinput node and an input of the first amplifier. At block 404, thesignaling processing system provides the first current to an output node(e.g., output node 258), a drain of the first transistor being coupledto the output node. At block 406, the signal processing system generatesa second current through a second resistive element (e.g., R4) bydriving, via a second amplifier (e.g., amplifier 244), a gate of asecond transistor (e.g., transistor 252) based on a voltage at a secondinput node (e.g., input node 213), and at block 408, provides the secondcurrent to the output node, a drain of the second transistor beingcoupled to the output node. In some aspects, the second resistiveelement may be coupled between the second input node and an input of thesecond amplifier.

In some aspects, the signal processing system may also generate a thirdcurrent (e.g., current 247) through a third resistive element (e.g., R2)by driving, via the first amplifier, a gate of a third transistor (e.g.,transistor 224) based on a voltage at a third input node (e.g., inputnode 274), and provide the third current to another output node (e.g.,output node 256). The signal processing system may also generate afourth current through a fourth resistive element (e.g., R3) by driving,via the second amplifier, a gate of a fourth transistor (e.g.,transistor 250) based on a voltage at a fourth input node (e.g., inputnode 211), and provide the fourth current to the other output node. Afifth resistive element may be coupled between the first and third inputnodes, and a sixth resistive element may be coupled between the secondand fourth input nodes.

In some aspects, a first voltage difference between the first input nodeand the third input node represents a first current flow, and a secondvoltage difference between the second input node and the fourth inputnode represents a second current flow. For example, the first currentflow may be a current through a first signal path (e.g., a path throughswitch 206) of an H-bridge amplifier (e.g., H-bridge amplifier 202), andthe second current flow may be a current through a second signal path(e.g., a path through switch 210) of the H-bridge amplifier.

In certain aspects, the signal processing system may sense an averagebetween voltages at the first input node and the third input node, andset a common-mode voltage associated with the first amplifier based onthe average between the voltages. In some aspects, the signal processingsystem may sense an average between voltages at the first input node andthe third input node, and set a voltage at a body terminal of atransistor used to implement the first resistive element based on theaverage between the voltages.

In certain aspects, the signal processing system may calibrate for amismatch between the first resistive element and the second resistiveelement by adjusting a resistance between the second input node and aninput (e.g., negative input) of the first amplifier. In some aspects,the signal processing system may compensate for an error current flow(e.g., error current due to parasitic capacitance 341) to the outputnode by selectively coupling one or more capacitive elements (e.g.,capacitive elements 350, 352, and/or 354) between the output node andone of a voltage rail node (e.g., voltage rail VDD/20) and a ground nodeof the circuit. In some aspects, the voltage rail node has a voltagethat is a fraction of a supply voltage for the first amplifier.

Within the present disclosure, the word “exemplary” is used to mean“serving as an example, instance, or illustration.” Any implementationor aspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects of thedisclosure. Likewise, the term “aspects” does not require that allaspects of the disclosure include the discussed feature, advantage, ormode of operation. The term “coupled” is used herein to refer to thedirect or indirect coupling between two objects. For example, if objectA physically touches object B and object B touches object C, thenobjects A and C may still be considered coupled to one another—even ifobjects A and C do not directly physically touch each other. Forinstance, a first object may be coupled to a second object even thoughthe first object is never directly physically in contact with the secondobject. The terms “circuit” and “circuitry” are used broadly andintended to include both hardware implementations of electrical devicesand conductors that, when connected and configured, enable theperformance of the functions described in the present disclosure,without limitation as to the type of electronic circuits.

The apparatus and methods described in the detailed description areillustrated in the accompanying drawings by various blocks, modules,components, circuits, steps, processes, algorithms, etc. (collectivelyreferred to as “elements”). These elements may be implemented usinghardware, for example.

One or more of the components, steps, features, and/or functionsillustrated herein may be rearranged and/or combined into a singlecomponent, step, feature, or function or embodied in several components,steps, or functions. Additional elements, components, steps, and/orfunctions may also be added without departing from features disclosedherein. The apparatus, devices, and/or components illustrated herein maybe configured to perform one or more of the methods, features, or stepsdescribed herein. The algorithms described herein may also beefficiently implemented in software and/or embedded in hardware.

It is to be understood that the specific order or hierarchy of steps inthe methods disclosed is an illustration of exemplary processes. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the methods may be rearranged. The accompanyingmethod claims present elements of the various steps in a sample order,and are not meant to be limited to the specific order or hierarchypresented unless specifically recited therein.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but are to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. A phrase referring to“at least one of” a list of items refers to any combination of thoseitems, including single members. As an example, “at least one of: a, b,or c” is intended to cover at least: a, b, c, a-b, a-c, b-c, and a-b-c,as well as any combination with multiples of the same element (e.g.,a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, andc-c-c or any other ordering of a, b, and c). All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

In certain aspects, means for generating and means for providing mayinclude an amplifier, such as the amplifier 220, amplifier 294, oramplifier 244. In certain aspects, means for sensing and means forsetting may include resistive elements, such as resistive elements 276,278 and/or a current source, such as the current source 288. In certainaspects, means for calibrating may include a resistor calibrationnetwork, such as the resistor calibration network 302 or 304. Means forcompensating may include a capacitive calibration network, such as thecapacitive calibration network 306 or 308.

What is claimed is:
 1. A circuit for signal processing, comprising: afirst amplifier; a first transistor, a gate of the first transistorbeing coupled to an output of the first amplifier and a drain of thefirst transistor being coupled to an output node of the circuit; a firstresistive element coupled between a first input node of the circuit andan input of the first amplifier, the first resistive element beingfurther coupled between the first input node and a source of the firsttransistor; a second amplifier; a second transistor, a gate of thesecond transistor being coupled to an output of the second amplifier anda drain of the second transistor being coupled to the output node of thecircuit; and a second resistive element coupled between a second inputnode of the circuit and an input of the second amplifier, the secondresistive element being further coupled between the second input nodeand a source of the second transistor.
 2. The circuit of claim 1,further comprising: a third transistor, a gate of the third transistorbeing coupled to another output of the first amplifier and a drain ofthe third transistor being coupled to another output node of thecircuit; a third resistive element coupled between a third input node ofthe circuit and another input of the first amplifier, the thirdresistive element being further coupled between the third input node anda source of the third transistor; a fourth transistor, a gate of thefourth transistor being coupled to another output of the secondamplifier and a drain of the fourth transistor being coupled to theother output node of the circuit; and a fourth resistive element coupledbetween a fourth input node of the circuit and another input of thesecond amplifier, the fourth resistive element being further coupledbetween the fourth input node and a source of the fourth transistor. 3.The circuit of claim 2, further comprising: a first current senseresistive element coupled between the first input node and the thirdinput node; and a second current sense resistive element coupled betweenthe second input node and the fourth input node.
 4. An audio systemcomprising the circuit of claim 3, the audio system further comprisingan H-bridge amplifier having: a first switch in a first path between avoltage rail and a speaker, the first path having the first currentsense resistive element; and a second switch in a second path betweenthe speaker and a reference potential node, the second path having thesecond current sense resistive element.
 5. The circuit of claim 3,further comprising: a fifth resistive element coupled to the first inputnode; a sixth resistive element coupled to the third input node; and acurrent source coupled to a node between the fifth resistive element andthe sixth resistive element, the node being further coupled to an inputcommon-mode node of the first amplifier.
 6. The circuit of claim 3,further comprising: a fifth resistive element coupled to the first inputnode; and a sixth resistive element coupled to the third input node,wherein a node between the fifth resistive element and the sixthresistive element is coupled to a body terminal of a transistor used toimplement the first resistive element.
 7. The circuit of claim 1,further comprising: a third amplifier having an input coupled to thedrain of the first transistor; and a third transistor having a gatecoupled to an output of the third amplifier, a source coupled to theinput of the third amplifier, and a drain coupled to the output node ofthe circuit.
 8. The circuit of claim 1, further comprising: a firstplurality of resistive elements coupled in series between the firstresistive element and the source of the first transistor; a secondplurality of resistive elements coupled in series between the secondresistive element and the source of the second transistor; and one ormore switches, each coupled between the input of the second amplifierand a respective node between two respective resistive elements of thesecond plurality of resistive elements.
 9. The circuit of claim 1,further comprising: a plurality of switches; and one or more capacitiveelements coupled to the output node, wherein the plurality of switchesare configured to selectively couple each of the one or more capacitiveelements to one of a voltage rail node and a ground node of the circuit.10. The circuit of claim 9, wherein the voltage rail node is configuredto receive a voltage that is a fraction of a supply voltage for thefirst amplifier.
 11. The circuit of claim 1, further comprising asumming amplifier having an input coupled to the drains of the firsttransistor and the second transistor.
 12. The circuit of claim 1,wherein the first transistor comprises a p-typemetal-oxide-semiconductor (PMOS) transistor, and wherein the secondtransistor comprises an n-type metal-oxide-semiconductor (NMOS)transistor.
 13. A method for signal processing, comprising: generating afirst current through a first resistive element by driving, via a firstamplifier, a gate of a first transistor based on a first voltage at afirst input node, wherein the first resistive element is coupled betweenthe first input node and an input of the first amplifier; providing thefirst current to an output node, a drain of the first transistor beingcoupled to the output node; generating a second current through a secondresistive element by driving, via a second amplifier, a gate of a secondtransistor based on a second voltage at a second input node, wherein thesecond resistive element is coupled between the second input node and aninput of the second amplifier; and providing the second current to theoutput node, a drain of the second transistor being coupled to theoutput node.
 14. The method of claim 13, further comprising: generatinga third current through a third resistive element by driving, via thefirst amplifier, a gate of a third transistor based on a third voltageat a third input node; providing the third current to another outputnode; generating a fourth current through a fourth resistive element bydriving, via the second amplifier, a gate of a fourth transistor basedon a fourth voltage at a fourth input node; and providing the fourthcurrent to the other output node.
 15. The method of claim 14, furthercomprising: sensing an average between the first and third voltages atthe first input node and the third input node; and setting a common-modevoltage associated with the first amplifier based on the average betweenthe first and third voltages.
 16. The method of claim 13, furthercomprising calibrating for a mismatch between the first resistiveelement and the second resistive element by adjusting a resistancebetween the second input node and the input of the first amplifier. 17.The method of claim 13, further comprising compensating for an errorcurrent flow to the output node by selectively coupling one or morecapacitive elements between the output node and one of a voltage railnode and an electric ground node.
 18. An amplifier circuit, comprising:an amplifier comprising a first switch, a second switch, a firstresistor coupled to the first switch, and a second resistor coupled tothe second switch; a first sensing path configured to convert a firstvoltage across the first resistor to a first sensed current; a secondsensing path configured to convert a second voltage across the secondresistor to a second sensed current; and a summing amplifier configuredto sum the first and second sensed currents.
 19. The amplifier circuitof claim 18, further comprising a processor configured to adjust a gainof the amplifier based on the summed currents.
 20. The amplifier circuitof claim 18, wherein the first and second switches are coupled to anoutput of the amplifier, and wherein the output is further coupled to aspeaker.